388 



manual of the mollusca. 

 Family YII. — Discinid^. 



Shell attaclied by a pedicle, passing tlirougli a foramen in tho 

 ventral valve ; valves not articulated ; minutely punctate. 



Fig. 195. Crania.* 



Fig. 196. Discina.\ 



Animal with a Mglily vascular mantle, fringed with long 

 horny setae ; oral arms curved backwards, returning upon them- 

 selves, and ending in small spires directed downwards, towards 

 the ventral valve. 



DisclNA, Lamarck. 



Syno'nyms, Orbicula, Sby. (not CuvierJ). Orbiculoidea 

 (elliptica), D'Orbigny. Schizotreta, Kutorga. 



Types, D. lamellosa, PL XV., Fig. 31. (=:D. ostreoides, 

 Lamarck.) 



Shell orbicular, horny ; upper valve limpet-like, smooth or 

 concentrically lamellose, apex behind the centre ; lower valve 

 flat or conical, with a sunk and j)erforated disk on the posterior 

 side ; interior polished ; lower valve with a central prominence 

 in front of the foramen. 



Animal transparent ; mantle lobes distinct all round ; labial 

 folds united, not extensile, ; alimentary canal simple, bent upon 

 itself ventrally, and terminating between the mantle-lobes on 

 the right side. There are four distinct adductor muscles as in 



* Dorsal valve, with the animal, seen by removing the mantle. 



+ The animal as seen on the removal of part of tlie lower mantle-lobe ; the extremities 

 of the labial arms are displaced forwards, in order to show their spiral terminations : 

 V is the expanded surface of the pedicle ; the mouth is concealed by the overhanging 

 cirri. The mantle-fringe is not represented. 



X The Orbicula of Cuvier was the Patella anomala, Miill (= Crania), as pointed out 

 by Dr. Fleming, in the " History of British Animals," 1828.. 



